The goal of this proposal is to determine the effect of IgA1 protease on secretory IgA antibody activity. Secretory IgA (SIgA) is the principal immunoglobulin isotype in the mucosal secretions of the body. SIgA is thought to play a major role in host defense at mucosal surfaces by inhibiting the colonization of potentially pathogenic microorganisms. A number of mucosal pathogens produce a protease that specifically cleaves the IgA1 subclass at the hinge region to produce Fab and Fc fragments. Despite the potential importance of IgA1 protease as a microbial virulence factor in host-parasite interactions at mucosal surfaces virtually nothing is known concerning the effect of cleavage on the antibody function of SIgA. Comparisons of antibody activity before and after cleavage with IgA1 protease cannot be readily achieved because (1) it is difficult to obtain high titer specific naturally occurring SIgA antibody from normal human serum or secretions and (2) IgA1 proteases synthesized by human mucosal pathogens have extraordinary specificity for only human, gorilla and chimpanzee IgA and will not cleave IgA from other animal species. The chimpanzee has been selected in the current proposal because (1) the chimpanzee can be immunized to induce high levels of specific SIgA antibody in breast milk and, (2) chimpanzee IgA is susceptible to cleavage by IgA1 proteases derived from human mucosal pathogens. The objective of this proposal is to determine whether IgA1 protease can interfere with the functional activity of SIgA antibody in the oral cavity. Accordingly, it is proposed to (1) determine the effect of IgA1 protease on the ability of SIgA antibody to bind to the cariogen, Streptococcus mutans. This will be accomplished by comparing the binding of anti-S. mutans SIgA antibody before and after treatment with IgA1 protease in an enzyme-linked immunosorbent assay. The effect of protease on SIgA antibody, before and after binding to S. mutans will be examined (2) determine the effect of IgA1 protease and the ability of SIgA antibody to agglutinate S. mutans. This will be accomplished by use of an agglutination assay in which the endpoint titer of the SIgA antibody will be compard before and after protease treatment and (3) determine the effect of IgA1 protease on the adherence inhibiting activity of SIgA antibody. This will be accomplished by comparing the effect of protease on the adherence of S. mutans to hydroxyapatite (HA) in the presence of SIgA antibody bound to bacteria or HA.